Reduce windows executable size

Question

I have a C++/MFC app on windows - dynamically linked it's only 60kb static it's > 3Mb.
It is a being distributed to customers by email and so needs to be as small as possible.

It statically links the MFC and MSCVRT libraries - because it is a fix to some problems and I don't want more support calls about missing libs - especially the very helpful 'application configuration is incorrect' one!

Is there anyway to strip a Windows exe of all the extra MFC stuff that is the dll but that I'm not using?
Or tell it to dynamically link MSVCRT (which must be present) but statically link the MFC dll which might not be?

Edit - thanks that got it down to 1.6Mb that will have to do!

Answer 1

You can't mix the CRT/MFC dlls. Going from memory...

As the other answer suggested, you can #define WIN32_LEAN_AND_MEAN and VC_EXTRALEAN. These probably won't help though. They tend to be about minimizing build time - not the final exe size.

Short of rebuilding MFC (Which is an option - you could rebuild it /Os, or if you are feeling really cheeky, /GL - but this will probably lead to more downstream fun - hopefully it's already built /Gy).

OK. Simple things to try. Build your app with /GL /Os /GF /Gy /GA. In the linker you more or less want /OPT:REF and /OPT:ICF and /LTCG.

I have to say - a release build from 30k to megabytes is a bit much. You could also pass /map: to the linker and see what's taking all that space - but that's very very tedius.

It almost sounds like MFC wasn't built with /Gy - but that would be surprising.

Answer 2

You can try Dependency Walker to check which DLLs that your static EXE file depends on, then if it depends on a library you are certain it exists at your client's machine, you can compile without it and reduce the size.

Answer 3

I'm not sure how to strip the executable, but another thought is to compress it, for example using upx, which will decompress it and run it in place... Does that reduce the size enough for you?

Answer 4

For programs using the CRT, you can use the technique in this video by Per Vognsen on achieving 3.5KB executables. Windows\System32\msvcrt.dll ships with every Windows since 95, so by linking to that, you needn't package the Visual C++ Redistributable with your app.

The basic process is:

1. Run Visual Studio's dumpbin on System32\msvcrt.dll and pipe it to a file
2. Run a simple filter (awk '{print $4}') to create a msvcrt.def file
3. Run VS's lib on msvcrt.def to generate msvcrt.lib
4. Disable default libraries in your project (/NODEFAULTLIB on the link command line)
5. Disable some Visual C++ checks (/GS- and remove any /RTC<x> flags)

Link against kernel32.lib and msvcrt.lib and voilà, your tiny executable has zero dependencies besides the OS.

(n.b.: To optimize for size (/O1), specify memset as an intrinsic as detailed here.)